Saturable reactor arc prevention circuit



April 1951 B. D. BEDFORD 2,547,614

smumu: REACTOR ARC PREVENTION cIRcuI'r Filed Sept. 24, 1948 2Sheets-Sheet 1 '2. LOAD Invent or: Burnice D. Bedfor-d,

His Attdr-neg.

April 3, 1951 B. D. BEDFORD 2,547,614

SATURABLE REACTOR ARC PREVENTION CIRCUIT Filed Sept. 24, 1948 2Sheets-Sheet 2 Inventor-z Burnice D. Bedfor-d, by Wm His Attrney.

Patented Apr. 3, 1951 SATURABLE REACTOR ARC PREVENTION CIRCUIT BurniceD. Bedford, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York Application September 24, 1948, Serial No.50,955

6 Claims. (01. 175-294) This invention relates to saturable reactors,

and more particularly to saturable reactors as an aid in switching.

' The physical and electrical properties of saturable core reactors arewell known. In essence, a saturable core reactor is merely an ordinaryreactor having at least one direct current exciting coil so that apredetermined flux density or degree of saturation of the reactor coremay be established. Therefore, if the flux induced within the core ofthe reactor is sufficient to cause saturation the impedance of thereactor may be quite small as compared to the reactor impedance when thecore is unsaturated. By controlling the direct current which flowsthrough the saturating coil or coils the impedance of the reactor may beadjusted within a predetermined range.

In power circuits the interruption or the opening of switches carryinghigh currents produces arcing which results in the burning and scarringof contact surfaces. Obviously, this is undesirable as it necessitatesconstant switch maintenance and replacement of contact surfaces. Thus,it would be advantageous to be able to interrupt high current circuitswithout establishing a destructive are. This invention prevents arcingin switching operations by utilizing the previously mentionedcharacteristic of saturable core reactors, that of impedance being afunction of core saturation. A saturable core reactor whose alternatingcurrent windings are of suflicient rating to withstand, for a shorttime, the full load current which is to be interrupted, is connected,originally in series with the load. The saturating winding of thereactor is excited from a rectifier whose source is a transformerconnected, in one particular form of the invention, across thealternating current load. Thus, the direct current through the excitingwinding of the reactor is dependent upon the alternating current voltageacross the load. In normal operation the reactor is short circuited by aswitch. When this switch is first opened to interrupt the current to theload an additional impedance in the form of the saturable core reactoris added to the circuit. The drop in load voltage due to this addedimpedance is manifest, through the action of the transformer andrectifier, in an increase in reactor impedance. This increase in reactorimpedance progresses until the unsaturated impedance of the reactor isin series with the load at which time the reactor and load circuit maybe completely open d without danger of arcing,

It is an object of this invention to provide a switching systemparticularly applicable for handling high currents which incorporates init a saturable core reactor.

Another object of this invention is to provide a new and simple meansfor allowing switches of low current rating to be utilized in highercurrent circuits.

Still another object of this invention is to provide new and improvedswitching means which will permit a decrease in switch maintenancecosts.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings, and its scope willbe pointed out in the appended claims.

In the drawings, Fig. 1 is a circuit diagram of a particular embodimentof the invention; Fig. 2 is a circuit diagram of an alternativeconstruction of the invention. Fig. 3 is a circuit diagram of anotheralternative construction of the invention.

Referring now to the drawing, there is shown in Fig. 1 by way ofexample, a circuit I having a load 2 conductively connected through aswitch 3 to the leads 4, 5 and 6. The leads 4 and 5 are coupled to apower source which is not shown in the figures. Normally, when theswitch 3 is opened the circuit to the load 2 is broken and if the loadcurrent is high an arc will be drawn between the switch contactsurfaces. In order to eliminate the are or decrease its intensity orduration to a point where the damage caused by it is negligible, asaturable core reactor I having alternating current windings 8 and adirect current saturating winding 9 wound on a magnetic core It may havethe alternating current windings 8 serially connected with anotherswitch I I. This combination of reactor windings 8 and switch II iscoupled in parallel with the switch 3. It can be seen from the drawingthat when the switches 3 and H are closed the alternating currentwindings 8 of the reactor 7 are short circuited; when the switch 3 isopen and the switch II is closed the windings 8 are in series with theload 2 and when both switches 3 and H are open no power is delivered tothe load 2.

The switches 3 and H may be incorporated in a unit i2 similar to the oneillustrated in Figs. 1 and 2 wherein the sequential operation of theswitches, switch 3 opening before switch II, is assured.

In Fig. 1 a transformer I3 is placed across the load 2 and its secondarywinding supplies a rectifier M, which in turn provides the directcurrent excitation for the saturating coil 9 of the re age across thetransformer I3.

3 actor I. It can be seen that the current within the coil 9 isdependent upon the voltage across the load 2, and the degree ofsaturation of the magnetic core Iii is therefore dependent upon the loadvoltage.

Assume that the switches 3 and. II are closed. Thus, the current flowsthrough the lead 5, through the switch 3, the lead 6, the load 2 and thelead 4, effectively removing the saturable core reactor I from thecircuit. It is desired to interrupt or open the circuit to the load 2.By energizing, in the illustrated cases, a solenoid I5, from a sourcenot shown, the switch 3 which is fixed to the movable shaft I6 of theswitching unit I2 is opened, but the switch II does not openimmediately. Thus, the reactor I is placed in series with theload 2. Itis to be remembered that a certain specific value of direct current isflowing through the saturating coil 9 of the reactor I and this value isdependent upon the voltage across the load 2 which is also the volt-Since the reactor I, no matter how saturated its core l may be, has acertain impedance there is a voltage drop through it, and the voltageacross the load 2 and the transformer I3 is decreased. This in turndecreases the current through the transformer I3, the rectifier l4 andthe saturating coil 9. As the saturating current decreases, the degreeof saturation of the reactor core III decreases, increasing theimpedance of the reactor I. When the impedance increases the voltagedrop due to the presence of the reactor I in the circuit increases, andagain the voltage across the load 2 and the transformer I3 decreases.This in turn results in a further decrease of direct current excitationof the core I0 and, therefore, a further increase in the inductiveimpedance of the reactor '5. As the impedance of the reactor I increasesthe total load connected between leads 4 and 5 is increased and,assuming a constant potential source, the load current is decreased.With proper adjustment of the impedance of the reactor I the loadcurrent may be decreased to a point Where the switch I I may be openedwithout danger of producing an arc. A delayed opening mechanism isincorporated in the unit I2 which allows a predetermined time to elapseafter the opening of switch 3 before switch II operates. It is shown inthe drawings by a plate II secured to the movable shaft I6 and whichengages the switch II. A capacitance I8 and a resistance I9 "which areserially connected have been introduced in parallel with the reactor Ito absorb the initial transients present when the switch 3 is firstopened.

A circuit 20 similar to the circuit I shown in Fig. 1 is illustrated inFig. 2, but in this case instead of the direct current-excitation of thesaturable reactor I being dependent upon the voltage across the load 2,it is dependent upon the current through the load. Again the reactor 1is placed in series with the load 2 but it is short circuited by theswitch 3. When the switch '3 is first opened the reactor I is placed inseries with the load 2. This causes a decrease in direct current throughthe saturating winding 9 by the action of a current transformer 2| and arectifier I4. The decrease in direct current excitation causes a furtherincrease in the inductive impedance of the reactor I which in turncauses a decrease in the load current. This action is cumulative untilthe load current has been decreased to a point where the switch II maybe opened without 'dan'ger of arcing.

It can be seen that in embodiments of the invention, illustrated inFigs. 1 and 2, even though in one case a voltage transformer and in theother a current transformer is used to control the direct currentthrough the saturating winding 9, the output of the transformers may beconsidered to be responsive to the amount of reactor impedance in serieswith the load 2; the greater the impedance of reactor '1 the smallerwill be the output of the transformers.

In the circuit 22, shown in Fig. 3, the output of the transformer 23 isnot a function of the impedance of the reactor R. In this embodiment ofthe invention a, third switch, 24, has been added to the switches 3 andII in a switching unit 25. Again the load 2 is conductively coupled tothe power leads 4 and 6, and the lead 6 is connected to the lead 5through the switch 3; the alternating current coils 8 of the saturablereactor I are serially connected to the switch I I and the coils 8 andswitch II are coupled in parallel with the switch 3. The transformer I0is connected in parallel with load 2 through the switch 24.

Thus, it can be seen that when the switches 3, 24, and II are closed thereactor 1 is shunted by the switch 3 and the load 2 is coupled directlyto the source through the leads 4 and 5. Since the switch 2 is closeddirect saturating current fiows through the coil 9 of the reactor 7causing the core it tobe highly saturated. This results in a lowimpedance of the saturable core reactor 1. The saturating current issupplied from the rectifier it which is coupled to the secondary of thetransformer 23.

It is desired to remove the load 2 from the line with a minimum ofarcing. To do this, in the illustrated case shown in Fig. 3, thesolenoid I5 is excited from a source not shown. The switches 3 and 24which are fastened to the shaft It will be opened, but the switch IIdoes not open immediately. Thus, with the opening of the switch 3 thesaturable core reactor I is placed in series with the load 2. Since thecore of the reactor 7 is highly saturated at the instant the switches 3and 2d are opened, the impedance of the reactor i will be very small andlittle or no arcing will occur at the switch 3. The opening of theswitch 24 removes the transformer 23 from the line. When this happensthe flow of saturating current through the coil 9 decays. stant theswitches 3 and 2 1 are opened a low impedance reactor I is seriallyconnected to the load. The saturating flux within the core I0 graduallydissipates itself and the impedance of the reactor I increases, causinga decrease in the load current. This increase in reactor impedancecontinues until the core it is unsaturated. The load current is then ofa sufficiently small value to allow the switch I I to be opened withoutdanger of excessive arcing.

While there has been shown and described particular embodiments of thisinvention it will be obvious to those skilled in the art that variouschanges and modifications can be made therein At the infore said secondswitch, a saturable core reactor, said second switch being seriallyconnected with an alternating current winding of said reactor, saidsecond switch and said alternating current winding coupled in parallelwith said first switch, and means operative coincidentally with theopening of said first switch for regulating the degree of saturation ofthe core of said saturable core reactor from an initial saturatedcondition to a desaturated condition.

2. In a high current circuit including a power source and a load coupledthereacross, the switching system comprising a first switch seriallyconnected with said source and said load, a second switch, means foropening said first switch before said second switch, a saturable corereactor, said second switch being serially connected with an alternatingcurrent winding of said reactor, said second switch and said alternatingcurrent winding coupled in parallel with said first switch, atransformer coupled with said load such that the output from saidtransformer is responsive to variations in impedance of said alternatingcurrent winding, rectifying means coupled to the output of saidtransformer and supplying a rectified signal to a direct currentsaturating winding of said reactor.

3. In a high current circuit including a power source and a load coupledthereacross, the switching system comprising a first switch seriallyconnected with said source and said load, a second switch, means foropening said first switch before said second switch, a saturable corereactor, said second switch being serially connected with an alternatingcurrent winding of said reactor, a capacitor and a resistance seriallyconnected and coupled in parallel with said alternating current winding,the combination of said second switch, said alternating current winding,said capacitor and said resistance being coupled in parallel with saidfirst switch, a, transformer coupled with said load such that the outputfrom said transformer is responsive to variations in impedance of saidalternating current winding, rectifying means coupled to the output ofsaid transformer and supplying a rectified signal to a direct currentsaturating winding of said reactor.

4. In a high current circuit including a power source and a load coupledthereacross, the switching system comprising a first switch seriallyconnected with said source and said load, a second switch, means foropening said first switch be fore said second switch, a saturable corereactor, said second switch being serially connected with an alternatingcurrent winding of said reactor, said second switch and said alternatingcurrent winding coupled in parallel with said first switch, atransformer coupled in parallel with said load and the output from saidtransformer being responsive to variations in the voltage across saidload, rectifying means coupled to the output of said transformer andsupplying a rectified signal to a direct current saturating winding ofsaid reactor.

5. In a high current circuit including a power source and a load coupledthereacross, the switching system comprising a first switch seriallyconnected with said source and said load, a second switch, means foropening said first switch before said second switch, a saturable corereactor, said second switch being serially connected with an alternatingcurrent winding of said reactor, said second switch and said alternatingcurrent winding coupled in parallel with said first switch, atransformer serially connected with said load and the output from saidtransformer being responsive to variations in the current through saidload, rectifying means coupled to the output of said transformer insupplying a rectified signal to a direct current saturating winding ofsaid reactor.

6. In a high current circuit including a power source and a load coupledthereacross, the switching system comprising a first switch seriallyconnected with said source and said load, a second switch, means foropening said first switch before said second switch, a saturable corereactor, said second switch being serially connected with an alternatingcurrent winding of said reactor, said second switch and said alternatingcurrent winding coupled in parallel with said first switch, atransformer, a third switch, said transformer and said third switchserially connected across said power source, said third switch beingcoupled to operate with said first switch, rectifying means coupled tothe output of said transformer and supplying a rectified signal to adirect current saturating winding of said reactor.

BURNICE D. BEDFORD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'I'ENTS Number Name Date 816,468 Hewlett May 27, 19061,571,304 Sindeband et al Feb. 2, 1926 1,611,687 Sindeband et a1 Dec.21, 1926 2,067,143 Logan Jan. 5, 1937 2,333,617 Smith Nov. 2, 19432,399,185 I-Iedding Apr. 30, 1946 FOREIGN PATENTS Number Country Date11,168 Great Britain Nov. 24, 1904 514,603 Germany Mar. 1, 1929 407,780Great Britain Mar. 29, 1934 357,349 Italy Mar. 11, 1938

